Base initiated depolymerization of polycarbonates to epoxide and carbon dioxide co-monomers: a computational study
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High-accuracy CBS-QB3(+) calculations were used to obtain the free energy barriers for several polycarbonates of interest to undergo alkoxide back-biting to give the corresponding epoxide and carbon dioxide. Free energy barriers to epoxide formation were modest for most polymeric alkoxides (12.7-17.4 kcal mol -1 ), and they were higher than for the same starting material to give cyclic carbonate (10.7-14.6 kcal mol -1 ). Poly(cyclopentene carbonate) differs: epoxide formation has a lower free energy barrier (13.3 kcal mol -1 ) than cyclic carbonate formation (19.9 kcal mol -1 ). These results explain why poly(cyclopentene carbonate) depolymerizes to cyclopentene oxide when treated with a strong base, whereas propylene and styrene polycarbonates depolymerize to their respective cyclic carbonates. Recycling via regeneration of the monomer represents the ideal method for producing material of the highest quality. 2013 The Royal Society of Chemistry.